Machines with electric drive systems, such as those including a continuously variable transmission (CVT) or more specifically, a split torque transmission, typically require that a machine be started from a zero engine speed state and prevent motion until an operator commands the machine to move. Before being able to accept operator commands, any electric drive system must complete a number of steps. For example, the status of the parking brake, any clutches, and/or any number of other systems may need to obtain a certain state before that step is completed and the new state is reached. Additionally, the steps may not occur in a truly linear fashion. For example, if after completing one step, a certain event occurs, the machine may revert to the previous step or may go to any other defined step. Although the subsequent step must be defined, it may not be a linear step. Further, fault conditions may be detected at any step, forcing the machine to go into a fault mode.
Prior art systems and methods exist for controlling a split torque transmission system. One such system and method is described in U.S. Pat. No. 5,682,315, entitled “Method and System for Controlling a Split Torque Transmission.” This system includes a hydrostatic transmission and a mechanical transmission. The system also includes a microprocessor, including a number of modules for performing the number of steps required to go from a zero engine state to a state where the machine is awaiting operator commands. The system, however, is not directed to electric CVT systems, which may require additional criteria to be met before moving between steps. Further, the system provides a fairly linear approach to the steps leading from a zero engine state to a state where the machine awaits operator command.
Thus, the prior art does not provide an efficient means to control initial operation of a work machine utilizing an electric continuously variable transmission. The present invention is directed to overcoming one or more of the problems or disadvantages associated with the prior art.